Fuse components of this type generally have a fusible link, which is dimensioned such that, if a maximum current is exceeded, the fusible link melts through and the current flow is consequently interrupted. The fusible link is usually fitted in a housing, so that a defect of the fusible link can often only be identified poorly from the outside. Moreover, identifying such a defect is usually made more difficult by the small dimensions of the fusible link.
U.S. Pat. No. 4,695,815 discloses an automobile fuse with an optical indicator. Here, a bulb is connected in parallel with the fusible link. If the fusible link is interrupted, the bulb lights up and in this way indicates the defect of the fuse. Also shown is an automobile fuse in which the bulb is arranged in a housing recess.
In the case of this arrangement, the bulb is freely accessible from the outside, so that there is the risk of damage being caused by external action. Additional protection by means of an enclosure, for example an encapsulating composition, requires additional effort, since it must be ensured that the encapsulating composition is thermally and mechanically adapted to the glass envelope of the bulb. Furthermore, there must be adequate adhesion between the glass envelope and the encapsulating composition and the ingress of moisture into the fuse must be prevented.
Moreover, bulbs are comparatively sensitive components, so that after they have been fitted for some time, even if not illuminated, there is the risk of a bulb defect, for example loss of the vacuum in the glass envelope or breakage of the filament. Such a defect, albeit rare, of the failure indicator of such a fuse must be especially avoided, since the user relies on the optical failure indicator, and therefore a burnt fuse with a defective failure indicator can only be found with great difficulty.